The present disclosure relates to a display device and a method for manufacturing the same, and in more particular relates to a display device including organic electroluminescent elements and a method for manufacturing the display device.
An organic electroluminescent element using electroluminescence (hereinafter referred to as “EL”) of an organic material has an organic layer which includes an organic hole transport layer and an organic light emitting layer laminated thereto between a lower electrode and an upper electrode each functioning as an anode or a cathode and has drawn an attention as a light emitting element that can emit high luminance light by a low voltage direct current drive.
An active matrix display device using organic electroluminescent elements as described above has a structure in which organic electroluminescent elements are provided on an interlayer insulating film which covers pixel drive circuits formed by using thin film transistors. Hence, in order to ensure an aperture ratio of a pixel, an organic electroluminescent element is advantageously formed to have a so-called upper-surface light extraction structure (hereinafter referred to as “top emission structure”) in which light is extracted from a side opposite to a substrate.
In the top emission structure, when a metal material, such as aluminum or silver, having superior light reflection characteristics is used as a lower electrode, an emission light extraction efficiency of an organic electroluminescent element can be improved. In this case, since aluminum and silver each have a high work function, the lower electrode formed therefrom functions as an anode. Hence, an upper electrode is formed to function as a cathode.
In addition, in the organic electroluminescent element having a top emission structure described above, an electric field is concentrated on a portion at which the distance between the lower electrode and the upper electrode is locally narrowed due to surface roughness of the lower electrode formed of a light-reflective metal material, and as a result, short-circuiting is liable to occur between the lower electrode and the upper electrode. Hence, the structure of the lower electrode has been proposed in which a light-reflective metal material layer and a buffer thin layer composed of an oxide of the light-reflective metal material are laminated to each other. According to the above proposal, by the structure described above, the surface roughness of the metal material layer is reduced by the buffer thin layer composed of the oxide, and the distance between the upper electrode and the lower electrode can be made uniform, so that short-circuiting caused by electric-field concentration can be prevented (see Japanese Unexamined Patent Application Publication No. 2002-216976).
In a display device in which organic electroluminescent elements are arranged on a substrate, an insulating pattern is provided for element isolation of the organic electroluminescent elements. This insulating pattern which has aperture windows to widely expose lower electrodes is provided to cover peripheries thereof and is formed from a photosensitive composition by patterning in a lithographic process. Hence, when the insulating pattern is formed, the lower electrodes are exposed to an alkaline developing solution used in a development treatment of the lithographic process. However, since aluminum and silver forming the light-reflective lower electrodes are a material having inferior resistance to an alkaline solution, the lower electrodes are damaged in this development treatment, and as a result, a lighting failure of a display may arise.
Accordingly, it is desirable to provide a display device which can prevent a lighting failure of a top-emission organic electroluminescent element caused by degradation of a lower electrode in a development treatment and a method for manufacturing the display device.